The ability to employ lasers in medical applications has existed for some time. Ultraviolet lasers can be employed to resurface a subject's cornea to enhance the subject's vision. Visible lasers can be employed to repair a subject's damaged retina. Indeed, vision enhancement in humans employing an ultraviolet excimer laser has become commonplace. Infrared lasers are more typically used in dermatology. Due to charring and other collateral damage effects, however, it has been difficult to employ some infrared lasers in surgical applications beyond those listed.
Infrared free electron lasers (FELs), on the other hand, can be employed in a variety of applications ranging from surgery on the optic nerve (Joos et al., Lasers Surg. Med. (2000) 27: 191) to tumor and tissue ablation, including FEL neurosurgery (Edwards et al., (1994) Nature 371: 416; Edwards, (1995) Opt. Eng. 34(5): 1524; Copeland et al., (2000) International Biomedical Symposium SPIE, San Jose, Calif.). See also, U.S. Pat. No. 5,403,306 to Edwards et al. A goal of laser ablation is to remove tissue by “cold” etching, a process in which the etch pattern is defined by the irradiating laser beam, leaving peripheral tissue free from collateral damage due to photothermal and photomechanical effects. Various features of an infrared FEL, such as wavelength and pulse structure of the FEL can be considered when an infrared FEL is employed in ablation.
Various prior art references disclose the use of lasers in surgery. For example, U.S. Pat. No. 5,423,803 to Tankovich et al. describes a process for removing a fraction of a superficial epidermal layer from human skin using a laser that emits in the infrared spectrum and has an emission time less than or equal to 50 ns. But in this application, before laser irradiation, a composition comprising chromophores is applied to the skin that is to be treated. By employing either ultrasound or a laser, these chromophores are inserted into the intracellular spaces of the tissue. This treated area of the skin is then irradiated by a laser beam having sufficient energy to ionize the chromophores (after optical breakdown).
Similarly, U.S. Pat. No. 6,086,580 to Mordon et al. discloses a laser treatment for the ablation of skin. The '580 patent also requires applying a composition to the surface to be ablated and is directed to the removal of warts, scars and other structures from the skin of a subject. The '580 patent notes that lasers that emit in the infrared spectrum can be employed in the method of the '580 patent, such as CO2 (10.6 μm), Er:YAG (2.94 μm), Ho:YAG (2.12 μm) and Nd:YAG (1.06 μm) lasers as well as lasers that emit in the visible spectrum, such as pulsed dye lasers (585 nm), ruby lasers (694 nm) and doubled Nd:YAG lasers (532 nm), however all of these methods and laser systems rely on the use of inserted chromophores.
These prior art methods and apparatuses, however, suffer the noted drawbacks. Additionally, FELs suffer from an additional drawback in that they typically require much space and are not table top laser systems. That is, the noted applications cannot be performed without large immobile laser systems (see, e.g. U.S. Pat. No. 5,795,351 to Clapham) and long and complex beam transport systems. In one aspect of the present invention, however, it is disclosed that efficient tissue ablation is not dependent on pulse structure, as was previously though. This observation facilitates the use, not only of any FEL meeting a given set of pulse structure-independent criteria in tissue ablation, but also the use of table top laser systems for this purpose. An ablation method employing a table top system would greatly enhance research in the fields of laser optics and optical engineering. Additionally, such a system would facilitate research in the area of medical applications of lasers and would assist in making laser-based surgery a more viable option for medical practitioners, as well as reducing the considerations of a patient, such as the need to transport the patient to a facility adapted for performing laser surgery.
With the advance of research into the application of light energy in medical fields, such as physical abrasion in oncology, orthopedics and dentistry, and industrial fields, such as precision machine engineering, semiconductor manufacture, and the like, demand has evolved for compact high-output table top laser systems that are adapted to accomplish these goals. Accordingly, a need exists for a method and apparatus employing a table top laser adapted for ablating material. Preferably, such an apparatus and method minimizes collateral damage to material surrounding the ablation site. A need also exists for an understanding of pulse structure features and/or conditions under which laser ablation of a material, preferably tissue, can be performed by employing an infrared FEL laser system or other infrared laser technology. The present invention solves these and other problems.